FIG. 1 shows a conventional evaporative emission control system (EVAP), generally indicated at 10, of a motor vehicle including a fuel vapor collection canister (e.g., a carbon canister) 12 and a normally closed canister purge valve 14 connected between a fuel tank 16 and an intake manifold 18 of an internal combustion engine 20 in a known fashion. A normally open canister vent valve 22 is in fluid communication between a vapor collection canister 12 and ambient atmospheric conditions via a filter 24. Under certain conditions, the purge valve 14 is opened and hydrocarbon vapors are drawn into the intake manifold 18 to be consumed by the engine 20.
With plug-in hybrid vehicles, vehicle operation may be such that the gas engine 20 may never need to be operated to charge the battery system. The vehicle fuel economy improves when the battery system is charged directly in the plug-in mode. However, if the gas engine is not operated, no vacuum is created at the intake manifold 18 for purging of the canister 12. Even without gas engine operation, the canister 12 will absorb hydrocarbons, after refueling or in hot weather, which will need to be purged.
Thus, there is a need for an evaporative emission control system to clean the canister at times when a gas engine of the vehicle is not operating.